Mouth sores, or oral ulcers, make it painful to eat and talk. Two of the most common types of recurrent mouth sores are fever blisters, also known as cold sores, and canker sores. Though similar, fever blisters and canker sores have important differences.

What Are Fever Blisters?

Fever blisters start as fluid-filled sores that most often appear on the outer lip borders, gums, or roof of the mouth. Fever blisters are usually painful, with pain usually preceding the appearance of the blister by a few days. The blisters rupture within hours and then crust over, lasting about seven to 10 days.

Why Do Fever Blisters Reoccur?

Fever blisters result from reactivation of the herpes simplex virus that otherwise lives dormant in many people. Reactivation of this virus can be caused by stress, fever, trauma, hormonal changes, and exposure to sunlight. When lesions reappear, they tend to form in the same location.

Are Fever Blisters Contagious?

Yes, the time from blister rupture until the sore is completely healed is the time of greatest risk for spreading the infection. The virus can spread to the afflicted person’s eyes and genitalia, as well as to other people.

How Are Fever Blisters Treated?

If caught early, fever blisters can be treated with an oral antiviral medication, such as acyclovir, to shorten the severity and duration of symptoms. There is no current cure, but you can take certain precautions to prevent spreading fever blisters, including:

  • Avoid mucous membrane contact when a lesion is present
  • Do not squeeze, pinch, or pick the blisters
  • Wash hands carefully before touching eyes, genital area, or another person

Note: Despite all caution, it is possible to transmit herpes virus even when no blisters are present.

What Are Canker Sores?

Canker sores, also called aphthous ulcers, are different than fever blisters and are the most common type of oral ulcer. They are small, shallow ulcers with a red border and white or yellow center that occur on the tongue, soft palate, or inside the lips and cheeks. Canker sores do not occur in the roof of the mouth or the gums. They are quite painful and usually last five to 10 days.

Who Gets Canker Sores, and What Causes Them?

While canker sores are common and can develop in anyone, they are seen more often in women and young adults or teenagers. The best available evidence suggests that canker sores result from an altered immune response in the area associated with stress, trauma, illness, hormonal changes, nutritional deficiency, or irritation. Acidic foods (e.g., tomatoes, citrus fruits, and some nuts) are known to cause irritation in some patients.

Are Canker Sores Contagious? How Are They Treated?

Because bacteria or viral agents do not cause canker sores, they are not contagious and cannot be spread to other parts of the body or to other people. Treatment is directed toward relieving discomfort and guarding against infection. A topical corticosteroid preparation such as triamcinolone dental paste (Kenalog in Orabase 0.1%®) can be helpful.

When Should I See a Doctor?

Consider consulting your doctor if a mouth sore has not healed within two weeks. Mouth sores become an easy way for germs and viruses to get into the body, so it is easy for infections to develop.

People who consume alcohol, smokers, smokeless tobacco users, chemotherapy or radiation patients, bone marrow or stem cell recipients, or patients with weak immune systems should also consider having regular oral screenings by a physician. The first sign of oral cancer is a mouth sore that does not heal.

Your doctor will most likely examine your head, face, neck, lips, gums, and high-risk areas inside your mouth such as under the tongue, the front and sides of the tongue, and the roof of the mouth or soft palate. If your doctor finds a suspicious lesion, they may recommend a biopsy to remove a piece of the it to be tested.

What Are Other Types of Oral Lesions?

Many other types of lesions can be seen in the mouth including infectious or inflammatory lesions, benign (noncancerous) and precancerous tumors, cancers, and even irregularities that can be considered normal. Some examples of other oral lesions include:

Leukoplakia—Leukoplakia is a thick, white-colored patch that forms on the inside of the cheeks, gums, or tongue. These patches are caused by excess cell growth and are common among tobacco users. They can result from irritations such as ill-fitting dentures or the habit of chewing on the inside of the cheek. Leukoplakia can progress to cancer.

Candidiasis—Candidiasis, or oral thrush, is a fungal infection that occurs when yeast reproduce in large amounts. It often causes white plaques that can be scraped off to reveal tender red areas underneath. It is common among denture wearers and most often occurs in people who are very young, elderly, debilitated by disease, or who have a problem with their immune system. People who have dry mouth syndrome or use oral steroid inhalers for asthma are also susceptible to the infection. Candida may flourish after antibiotic treatment, which can decrease normal bacteria in the mouth.

Hairy tongue—Hairy tongue is a harmless condition that causes the top of the tongue to develop a furry yellow to dark brown coating. It is caused by the buildup of dead skin on tiny projections, or papillae, that cover the top of the tongue. Poor oral hygiene, chronic oral irritation, or smoking can cause this condition. Hairy tongue is often treated with a toothbrush or special tongue scraper to help remove the dead skin.

Torus palatinus—Torus palatinus is a hard, bony growth in the center of the roof of the mouth (palate).  It commonly occurs in early adulthood, more often in women. Both environmental factors, such as teeth grinding, and genetic factors may contribute to its formation. While rarely needing treatment, a torus palatinus may be removed in order to fit dentures properly.

Mucocele—Mucoceles are soft mucous-filled nodules that are commonly found on the inside of the lower lip. These usually occur from a bite to the lip that injures a minor salivary gland, causing a spillage of mucous and creating a small lump. Mucoceles can rupture or “pop” but often come back.

Oral cancerOral cancer may appear as a white or red patch of tissue in the mouth, or a small ulcer that looks like a common canker sore. Other than the lips, the most common areas for oral cancer to develop are on and under the tongue. Other symptoms include a firm lump or mass that can be felt inside the mouth or neck; pain or difficulty with swallowing, speaking, or chewing; any wart-like mass; hoarseness that lasts for more than two weeks; or any numbness in the oral/facial region.

Dental trauma—Injury to the teeth, gums and/or nearby soft tissue such as the lips and tongue can cause a mouth sore, for instance, accidentally biting the inside of your mouth or cheek.

How Can I Prevent Mouth Sores?

You can take certain steps to help prevent mouth sores including:

  • Stop smoking
  • Reduce stress
  • Avoid injury to the mouth caused by hard tooth brushing, hard foods, braces, or dentures
  • Chew slowly to avoid biting your tongue or lip
  • Practice good dental hygiene, including regular visits to the dentist
  • Eat a well-balanced diet
  • Identify and eliminate food sensitivities
  • Drink plenty of water
  • Avoid very hot food or beverages
  • Follow nutritional guidelines or talk to your doctor about the use of multivitamin supplements

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The information on is provided solely for educational purposes and does not represent medical advice, nor is it a substitute for seeking professional medical care.